Q1. The potential distribution across a suspension insulator string is:
A) Uniform
B) Non-uniform
C) Linear
D) Constant
Ans: B
Q2. The electric field intensity across the unit nearest to the line is:
A) Maximum
B) Minimum
C) Equal to middle unit
D) Zero
Ans: A
Q3. Non-uniform potential distribution in a string of suspension insulators is due to:
A) Shunt capacitances
B) Resistance of porcelain
C) Weight of discs
D) None
Ans: A
Q4. The capacitance between metal parts of adjacent discs is called:
A) Mutual capacitance
B) Shunt capacitance
C) Self-capacitance
D) Line capacitance
Ans: A
Q5. Capacitance between line conductor and metal fitting of uppermost unit is:
A) Line-to-earth capacitance
B) Capacitance to line
C) Capacitance to earth
D) Self-capacitance
Ans: B
Q6. String efficiency is defined as:
A) (Voltage across string / n × average voltage per unit) × 100
B) (Voltage across string / n × voltage across bottom unit) × 100
C) (Voltage across string / n × maximum voltage per unit) × 100
D) (n × voltage across string / total voltage) × 100
Ans: C
Q7. For a perfectly uniform voltage distribution, string efficiency is:
A) 100%
B) 0%
C) 50%
D) 75%
Ans: A
Q8. In a string of suspension insulators, the lower discs have:
A) Higher voltage stress
B) Lower voltage stress
C) Equal stress
D) None
Ans: A
Q9. String efficiency can be improved by:
A) Grading the insulators
B) Using guard rings
C) Both A and B
D) None
Ans: C
Q10. Guard ring is used to:
A) Improve voltage distribution
B) Support discs
C) Reduce sag
D) None
Ans: A
Q11. Guard ring increases the:
A) Capacitance of upper units
B) Capacitance of lower units
C) Capacitance of all discs
D) None
Ans: A
Q12. The ratio of maximum to minimum voltage across insulator units indicates:
A) Non-uniformity
B) String efficiency
C) Flashover voltage
D) None
Ans: A
Q13. The dielectric strength of porcelain is approximately:
A) 30 kV/cm
B) 100 kV/cm
C) 10 kV/cm
D) 3 kV/cm
Ans: A
Q14. Cap and pin type insulator is used for:
A) Suspension type
B) Strain type
C) Both
D) None
Ans: C
Q15. The creepage distance is:
A) Surface distance between line and earth
B) Air distance
C) Direct distance through porcelain
D) None
Ans: A
Q16. Longer creepage distance is required in:
A) Polluted atmosphere
B) Clean air
C) Desert region
D) None
Ans: A
Q17. In polluted areas, preferred insulator type is:
A) Composite or long rod
B) Pin type
C) Strain
D) None
Ans: A
Q18. For 400 kV transmission, typical creepage distance is around:
A) 900–1000 mm
B) 2500–3000 mm
C) 600–800 mm
D) 400 mm
Ans: B
Q19. The electric field is highest near:
A) Line conductor
B) Earth end
C) Center
D) None
Ans: A
Q20. Unequal potential distribution causes:
A) Premature flashover
B) Increased efficiency
C) Less corona
D) None
Ans: A
Q21. Field distribution along string can be made uniform by:
A) Metal grading rings
B) Parallel resistors
C) Both
D) None
Ans: C
Q22. The capacitance between metal parts and earth is known as:
A) Capacitance to earth
B) Self-capacitance
C) Mutual
D) None
Ans: A
Q23. String efficiency increases if:
A) Mutual capacitance decreases
B) Shunt capacitance decreases
C) Line capacitance decreases
D) None
Ans: B
Q24. For n identical insulators, potential across the bottom unit is:
A) Highest
B) Lowest
C) Equal
D) Zero
Ans: A
Q25. The voltage distribution across insulator string is analyzed using:
A) Capacitance model
B) Inductance model
C) Resistance model
D) None
Ans: A
Q26. If capacitance to earth = k × mutual capacitance, then uniformity improves with:
A) Smaller k
B) Larger k
C) k = 1
D) None
Ans: A
Q27. When guard rings are used, potential distribution becomes:
A) More uniform
B) Less uniform
C) Non-linear
D) None
Ans: A
Q28. The leakage current flows:
A) Over surface of insulator
B) Through porcelain
C) Through pin
D) None
Ans: A
Q29. The leakage current causes:
A) Heating and surface tracking
B) Corona
C) Flashover reduction
D) None
Ans: A
Q30. Flashover voltage is:
A) Voltage that causes spark over surface
B) Voltage that punctures insulator
C) Normal working voltage
D) None
Ans: A
Q31. Puncture voltage is:
A) Voltage that breaks porcelain
B) Flashover voltage
C) Same as breakdown
D) None
Ans: A
Q32. A good insulator should have:
A) Puncture voltage > Flashover voltage
B) Flashover > Puncture
C) Both equal
D) None
Ans: A
Q33. The puncture strength is usually:
A) 2–3 times flashover strength
B) Less
C) Equal
D) None
Ans: A
Q34. Pin type insulators are used up to:
A) 33 kV
B) 66 kV
C) 132 kV
D) None
Ans: A
Q35. Suspension insulators are preferred above:
A) 33 kV
B) 66 kV
C) 11 kV
D) None
Ans: A
Q36. Strain insulators are used:
A) At dead ends
B) In-line supports
C) At top of pole
D) None
Ans: A
Q37. The potential distribution depends on:
A) Capacitance ratios
B) Frequency
C) Temperature
D) None
Ans: A
Q38. Artificial grading uses:
A) Metal rings or resistors
B) Porcelain thickness
C) Air gap
D) None
Ans: A
Q39. The capacitance of insulator units increases with:
A) Larger surface area
B) Smaller distance
C) Both
D) None
Ans: C
Q40. In high-voltage lines, the lower insulator unit often fails first due to:
A) Higher potential stress
B) Mechanical tension
C) Dust
D) None
Ans: A
Q41. The dielectric loss angle of porcelain is about:
A) 1°–2°
B) 10°
C) 30°
D) 0°
Ans: A
Q42. The capacitance between line and earth is typically in the range:
A) 5–10 pF per unit
B) 1–2 µF
C) 0.1–1 pF
D) None
Ans: A
Q43. The effective voltage across the string is sum of:
A) Individual unit voltages
B) Line voltages
C) Earth voltages
D) None
Ans: A
Q44. The equalizing ring (grading ring) redistributes:
A) Electric field
B) Temperature
C) Current
D) None
Ans: A
Q45. Composite insulators are made of:
A) Fiberglass core + polymer sheath
B) Porcelain only
C) Glass only
D) None
Ans: A
Q46. Composite insulators are preferred because:
A) Lightweight & hydrophobic
B) Costlier
C) Poor mechanical strength
D) None
Ans: A
Q47. The electric field near hardware fittings is reduced by:
A) Grading rings
B) Thicker porcelain
C) Coating
D) None
Ans: A
Q48. The leakage current increases with:
A) Humidity and pollution
B) Dry air
C) Altitude
D) None
Ans: A
Q49. The wet flashover voltage is:
A) Lower than dry flashover
B) Higher
C) Equal
D) None
Ans: A
Q50. Dry flashover voltage of pin type insulator (11 kV system) ≈
A) 35 kV
B) 10 kV
C) 66 kV
D) 3 kV
Ans: A
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